I took my CLD test a week or so ago, and figured I'd post my thoughts about it since it may help someone else. I won't say what the actual application was, since NI does not allow it, but I'll make some generic comments and try to show where I made my mistakes. I won't know if I passed for a week or two, but based on the scoring system I think I will likely be a couple points short. I only had the application 25% functional at best, although all the basic framework was in place. I also made two errors early on that cost me too much time and kept me from having any chance of finishing. I suspect I only got 5 points on functionality, and maybe 12-14 on Style and 8 on documentation. That would put me at 25-27 points needing 30 to pass.
My first comment is that time management is critical. Basically, I just ran out of time (which is what I suspected would happen) so the first thing people need to take from this is that it's going to be nearly impossible to finish. Focus on getting as much of the application functional as possible and get as much documentation done as you can to boost your points. Stub the more difficult sections of code and get the easy stuff done first. The application was about 50% harder than any of the examples, so if you can't do every example in three hours or less, then you will likely not get the full 15 points for functionality and may even get half of that or less.
Second, take the most difficult concept from each of the examples and roll them into a single application to practice with. The Security System used an event structure to handle all the front panel events, plus had a logfile. The Car Wash used a pauseable timer in a state machine. Put the two together, and bury that state machine in the consumer loop of a producer/consumer pattern that needs to initialize itself from a configuration file. To do it, you need to have a timeout case on the event structure in the producer loop that will ping the consumer periodically and allow it to check the timer. This is where I made one of my critical errors. When you setup the consumer loop, you need to handle the events from the producer in the context of the state machine. That means you have two case structures, one inside the other, to handle all the possible combinations of State and Event. The mistake I made was making the State case the outside one and putting the Event case on the inside. There were many Events that could be ignored depending on the State, so it made a lot more sense to do it the other way. I didn't figure this out until I was knee deep in the code however, and with the 4 hour time limit I couldn't go back and fix it.
Third, make sure you understand all the basic concepts completely, including the subtle things. For example, make sure you understand all the implications of auto-indexing two arrays into a for loop. I was passing an empty input array into a for loop to use as the type definition for a bundle-by-name. Because the size of the array was zero, the loop never executed even though the second auto-indexed input was an array of 4 items. It was a dumb mistake that cost me a fair bit of functionality points since I didn't see the bug until it was too late to troubleshoot it.
Finally, don't even look at the solutions to the practice examples. None of them use a producer/consumer design pattern and it's almost guaranteed you will need to use one for the real test. Instead, try and modify the examples to make them require a producer/consumer by adding functionality. For example, modify the Car Wash to require that it repond to the vehicle positioning switches within 10 miliseconds and have it load the car wash types and sequences from a configuration file instead of hard coding them.
That's all I can think of at the moment. Hopefully this will help any of you that are thinking of taking the CLD. Feel free to email me if you have questions, but I won't talk about any of the specifics of the exam since I'm not suppossed to. One final thought is that when I went home, I sat down and coded the application from memory and it took me 7.5 hours to get it completely 100% functional. And that didn't include documenting it. I think it's one of the hardest exams I've ever had to take.
Jim Smith
